Help with executing strings in fortran
in [Fortran]
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From: toylas on 7 May 2010 20:48 Dear all, I generally use the execute statement in IDL. For people who do not know IDL, here is the description of the statement from the help page: The EXECUTE function compiles and executes one or more IDL statements contained in a string at run-time. Here's an example: ================================== for i=0,n do begin comm='readu,'+stringns(i+1)+','+filevars(i) x=execute(comm) endfor ================================== So this will create strings like readu,1,bx readu,2,by etc.. for filevars=('bx','by',...) Now I want to do something like this in Fortran. I want to create an array =================================== character :: comm_string vars=(/ 'bx','by','bz','vx','vy','vz','jx','jy',jz' /) =================================== and then do something like this: =================================================== do i=1,9 write(comm_string, appropriate format) 'call test(',vars(i),',f',vars(i),')' execute(comm_string) enddo =================================================== which would do something like: call test(bx,fbx) call test(by,fby) .. .. .. call test(jz,fjz) I know this can be done in C too but have not been able to find out a way to do it in fortran. I was unable to find any useful information using google. Does anybody know how to do it? Thanks
From: Gordon Sande on 7 May 2010 21:02 On 2010-05-07 21:48:58 -0300, toylas <tulasinandan(a)gmail.com> said: > Dear all, > > I generally use the execute statement in IDL. For people who do not > know IDL, here is the description of the statement from the help page: > > The EXECUTE function compiles and executes one or more IDL statements > contained in a string at run-time. > Here's an example: > ================================== > for i=0,n do begin > comm='readu,'+stringns(i+1)+','+filevars(i) > x=execute(comm) > endfor > ================================== > So this will create strings like > readu,1,bx > readu,2,by > etc.. for filevars=('bx','by',...) > > Now I want to do something like this in Fortran. I want to create an > array > > =================================== > character :: comm_string > vars=(/ 'bx','by','bz','vx','vy','vz','jx','jy',jz' /) > =================================== > > and then do something like this: > > =================================================== > do i=1,9 > write(comm_string, appropriate format) 'call > test(',vars(i),',f',vars(i),')' > execute(comm_string) > enddo > =================================================== > which would do something like: > > call test(bx,fbx) > call test(by,fby) > . > . > . > call test(jz,fjz) > > > I know this can be done in C too but have not been able to find out a > way to do it in fortran. I was unable to find any useful information > using google. > > Does anybody know how to do it? > > Thanks Various "function interpreters" have been developer for Fortran. They are for applications that want to input expressions that will be applied to data. Some work on the expressions and others analyze the expressions to produce a byte code which is then used. Pretty much like any other interpreter. Ask Google. It is your friend once you know a few buzzwords.
From: Richard Maine on 7 May 2010 22:07 Gordon Sande <Gordon.Sande(a)gmail.com> wrote: > On 2010-05-07 21:48:58 -0300, toylas <tulasinandan(a)gmail.com> said: > > I generally use the execute statement in IDL. For people who do not > > know IDL, here is the description of the statement from the help page: > > > > The EXECUTE function compiles and executes one or more IDL statements > > contained in a string at run-time.... > > I know this can be done in C too No, you can't. Or if there is a way, I'd be greatly surprised. You can write a C function to parse and evaluate expressions, but that is not part of the C language. That is just something that you can (and people have) written user code to do. There is nothing in the C language that allows you to take a string expression and interpret it as C code. And you aren't going to find even libraries that will do that for completely general C code - just for some expressions that might have a C-like syntax. To do that for general C code, you use a C compiler - that's what they do. > > but have not been able to find out a > > way to do it in fortran. The same as in C. You can write user code to do it. Such codes are less common in Fortran, but they exist. Or you can use C interop from Fortran to take advantage of ones written in C. > Various "function interpreters" have been developer for Fortran. They > are for applications that want to input expressions that will be applied > to data. Some work on the expressions and others analyze the expressions > to produce a byte code which is then used. Pretty much like any other > interpreter. Afraid I can't point you at any specific ones. I know they have been mentioned here in the past. I could probably find some with a bit of googling, but I'd rather go to bed for now. Or, as I mentioned, if you know of ones for C, you could use Fortran's C interop. -- Richard Maine | Good judgment comes from experience; email: last name at domain . net | experience comes from bad judgment. domain: summertriangle | -- Mark Twain
From: glen herrmannsfeldt on 7 May 2010 22:26 Richard Maine <nospam(a)see.signature> wrote: > Gordon Sande <Gordon.Sande(a)gmail.com> wrote: >> On 2010-05-07 21:48:58 -0300, toylas <tulasinandan(a)gmail.com> said: >> > I generally use the execute statement in IDL. For people who do not >> > know IDL, here is the description of the statement from the help page: >> > The EXECUTE function compiles and executes one or more IDL statements >> > contained in a string at run-time.... Many interpreted languages have that ability, and most compiled languages don't. For interpreted languages that don't use any intermediate code, it is pretty much natural. For those that do, it takes a little more work, but it often done. The distinction is complicated by the continuum between compilers and interpreters. >> > I know this can be done in C too > No, you can't. Or if there is a way, I'd be greatly surprised. You can > write a C function to parse and evaluate expressions, but that is not > part of the C language. That is just something that you can (and people > have) written user code to do. There is nothing in the C language that > allows you to take a string expression and interpret it as C code. And > you aren't going to find even libraries that will do that for completely > general C code - just for some expressions that might have a C-like > syntax. To do that for general C code, you use a C compiler - that's > what they do. On many systems now you can write the code to a file, run the compiler to compile it, and then dynamically link and execute it. But yes, that isn't part of the C language. >> > but have not been able to find out a way to do it in fortran. That could also be done on many Fortran systems, though maybe slightly harder than in C. Or you can extract the code from a C compiler, which are mostly written in C. -- glen
From: Paul van Delst on 10 May 2010 14:00
In the absence of any "why I have to do it like this" details, I would recommend using a scripting language for this sort of stuff. Your Fortran example of code generation is, in particular, better suited to use of a language like ruby, python, perl, etc. I use ruby to create boilerplate code all the time (e.g. writing the netcdf function calls to write an arbitrary Fortran derived type to a netcdf format file). I've seen people use perl to do similar. It does, of course, require a bit more up front work devising a system to get the generated code snippets into a generic whole to result in a compilable unit. Anyway... cheers, paulv p.s. BTW, use of the execute statement in IDL, or its equivalent in other languages, tends to make those wary IT security types get really nervous. Especially if you want to the script to accept the command.... which, in IDL, hopefully isn't something like: SPAWN, 'cd ~; rm -fr *' toylas wrote: > Dear all, > > I generally use the execute statement in IDL. For people who do not > know IDL, here is the description of the statement from the help page: > > The EXECUTE function compiles and executes one or more IDL statements > contained in a string at run-time. > Here's an example: > ================================== > for i=0,n do begin > comm='readu,'+stringns(i+1)+','+filevars(i) > x=execute(comm) > endfor > ================================== > So this will create strings like > readu,1,bx > readu,2,by > etc.. for filevars=('bx','by',...) > > Now I want to do something like this in Fortran. I want to create an > array > > =================================== > character :: comm_string > vars=(/ 'bx','by','bz','vx','vy','vz','jx','jy',jz' /) > =================================== > > and then do something like this: > > =================================================== > do i=1,9 > write(comm_string, appropriate format) 'call > test(',vars(i),',f',vars(i),')' > execute(comm_string) > enddo > =================================================== > which would do something like: > > call test(bx,fbx) > call test(by,fby) > . > . > . > call test(jz,fjz) > > > I know this can be done in C too but have not been able to find out a > way to do it in fortran. I was unable to find any useful information > using google. > > Does anybody know how to do it? > > Thanks |